Portable radio transmitter and receiver devices have been provided which are of a size to be held in the hand of a user. These devices have had the circuitry provided compactly on a small printed circuit board which has made servicing and repair difficult. It has been proposed to provide the circuit as plug-in modules, but it has not been possible to provide the required circuitry within the space limits by using known technology. Also, there is a problem of inserting small closely spaced modules and replacing the same as may be required for servicing and repair.
Radio transmitter and receiver devices must operate at prescribed frequencies, and must be held to such frequencies with very small tolerances. This makes it necessary to use frequency controlling elements, such as piezoelectric crystals, and to further provide fine adjustment of the tuning circuits, as by use of an adjustable tuning coil. Prior module construction has not made it possible to provide miniature channel tuning elements within the allotted space, and which can be tuned as required.